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The detector, whose scheme is shown in Fig. 2.25, you can collect only for a few minutes. It consists of a small number of elements:

  • two almost identical LC oscillators, performed on the elements DD1.1-DD1.4;
  • the detector according to the scheme of doubling the rectified voltage on the diodes VD1, VD2;
  • high impedance (2 ohms) headphones BF1.

Change sound headphones and indicates the presence of under the coil antenna of a metal object.

Fig. 2.25. A schematic diagram of a simple metal detector on the chip UCY7400

Schematic diagram

Generator, assembled on the elements DD1.1 and DD1.2, frequency snowspeeders resonance of the series resonant circuit L1C1 configured on the frequency 465 kHz. Can be used successfully finished elements, for example, from the filter FC superheterodyne receiver.

The frequency of the second generator (DD1.3, DD1.4) is determined by two components:

  • the inductance of the coil antenna L2 (30 turns of wire PEL of 0.4 mandrel 200 mm diameter);
  • the capacitance of the variable capacitor C2, allowing before searching to configure the detector to the detection of objects of a certain mass.

The beats resulting from the mixing of the oscillations of the two oscillators, are detected by diodes VD1, VD2, filtered by capacitor C5 and act on head phones BF1.

Design and details

The entire device can be assembled on a small PCB, which allows powered by a flat battery flashlight make it very compact and comfortable to handle.

The repetition of the detector it is possible to use chip K155LA3, any high-frequency germanium diodes and KPE from radio "Mountaineer".

Author: A. Janeczer